1. Field of Invention
The present invention relates to a damascene process. More particularly, the present invention relates to a method of fabricating a metal interconnect for a semiconductor device.
2. Description of Related Art
Electromigration is the movement of the ions in a conductor (such as Cu) in response to the passage of current through it. These ions are moved "downstream" by the force of the "electron wind". A positive divergence of the ionic flux leads to accumulation of vacancies, forming a void in the metal. Such voids may ultimately grow to a size that results in an open-circuit failure of the conductor.
FIGS. 1A-1B are schematic, cross-sectional views of a conventional Cu damascene process.
Referring to FIG. 1A, a dielectric layer 101 is deposited over a substrate 100. The dielectric layer 101 is patterned to form an opening 102 exposing the substrate 100. The opening 102 is filled with a conductive plug. The conductive plug conventionally comprises a conformal titanium nitride (TiN) layer 104 and a copper (Cu) layer 106 in the opening 102.
Referring to FIG. 1B, a silicon nitride layer 108 and a plasma-enhanced oxide layer 110 arc sequentially deposited over the dielectric layer 101. The plasma-enhanced oxide layer 110 is provided for the next damascene process.
Still referring to FIG. 1B, the Cu layer 106 directly contacts the overlying silicon nitride layer 108 in this damascene process. After performing a reliability test on this Cu layer 106, it is found that ions of such a Cu layer 106 migrate in the direction of the overlying silicon nitride layer 108, leading to accumulation of vacancies which form a void (not shown) in the Cu layer 106. Such voids may ultimately grow to a size that results in an open-circuit failure of the Cu layer 106.